In a known ignition system disclosed in German Pat. publication DT-AS 2,244,781, the ignition current required to build up a magnetic field in the ignition coil is controlled by means of a closure control circuit. The closure control circuit operates in response to a sensor which furnishes a signal over a predetermined angular rotation of a shaft of the engine. In the known system, the closure angle is varied as a function of engine speed, the closure angle decreasing with decreasing engine speed and increasing with increasing engine speed. This arrangement has the disadvantage that ignition current control operates only as a function of engine speed. Changes in ignition voltage and spark duration for different loads of the engine, for example for increased capacitive loads or as a result of dirty spark plugs are not taken into consideration.